PRAGUE, Czech Republic -- Czech leaders expressed deep concern over a neo-Nazi demonstration and an assault on a family during the weekend, Prague Radio said.

More than 500 far-right militants staged a rally Saturday in the northern Czech town of Usti nad Labem that some police officials suggested was aimed at marking the anniversary of Nazi leader Adolf Hitler's birthday, which falls on Monday, the radio said.

Outgoing Czech Prime Minister Mirek Topolanek and Czech President Vaclav Klaus spoke against what they described as growing extremism in the country.

The two leaders condemned the attack on a Romany couple and their 2-year-old daughter Saturday. Unidentified assailants in the northeastern Czech Opava region set the family's home on fire with a petrol bomb, police said.

Doctors in a hospital in Ostrava Monday said the baby was in a critical condition with burns over 80 percent of her body. Her mother, 27, was seriously injured and her father undewent surgery to treat extensive burns.